Controlling manganese ion impurities in permonosulfate bleaching



United States Patent O No Drawing. Filed July 28, 1959, Ser. No. 830,1982 Claims. (Cl. 84111) This invention relates to a method of effectivelybleaching with a permonosulfate composition in the presence of manganeseions and, more particularly, to a bleaching method wherein anydiscolorationinduced by manganese ions oxidized to a high valence stateby permonosulfate compositions is avoided or removed.

Alkali metal permonosulfates are known as bleaching agents, beingstronger oxidizing agents than hydrogen peroxide and many other commonlyused per compounds. The use of permonosulfates in tap water presents aproblem because some tap water supplies contain manganese in amounts of0.1 p.p.m. or more and these strong oxidizing agents promote theformation of manganese ions in their higher oxidized states (+3 and .+4)and these manganese ions impart a yellow color to the material beingtreated. Discoloration by manganese oxidized to the +3 and +4 state isapparent in some tap water which has been found to contain about 0.1p.p.m. or more manganese. Analysis has shown that ordinary tap waterrarely contains more than 0.2 p.p.m. manganese. Discoloration isnoticeable when white cloth is laundered or white porcelain is cleansed.

It has been found that yellow-colored manganese ions h can be reduced tothe colorless state (+2) even inthe presence of alkali metalpermonosulfates through the use of perhydrates as reducing agents.Additionally, it has been found that permonosulfates and perhydrates aremutually tolerant and that solutions containing these compounds incertain ratios will bleach materialsdiscolored by yellow-coloredmanganese ions. Further, it has been determined that solid mixtures ofalkali metal permonosulfates and perhydrates may be used alone orincluded in various conventional detergent and cleansing formulationsand that these formulations ni-ay .be used in virtually any watersupply, being unafiected by either the presence of manganese ions or thehardness of the water.

It is an object of the present invention to provide an effective methodfor bleaching solutions containing an alkali metal permonosulfate andmanganese ions.

It is another object of the present invention to'provide' a method ofbleaching in solutions containing an alkali metal permonosulfate andmanganese ions without discolorin-g the material being treated.

It is still another object of the present invention to provide a methodfor removing the discoloration caused by manganese ions oxidized to ahigh valence state.

Some water supplies contain 0.1 p.p.m. or more manganese, usually in thecolorless state as Mn++. Manganous ions are colorless and are usuallynot detrimental in bleaching or laundering solutions because hydrogenperoxide and other conventional bleaching agents will not oxidizemanganese to the yellow'colored state of +3 and +4.

In the below table, the various concentrations of Mn were obtained byadding increasing amounts of manganous sulfate to distilled water andthe below bleaching composition was added to each solution.

The term Oxone refers to a mixture of KHSO KHSO and K 80 in moleproportions of 221:1, and KHSO constitutes about 50% by weight of themixture.

I Ce,

Percent Oxone 35 Sodium sulfate 20 Sodium metasilicate 5 Sodiumcarbonate. 20 Tetrasodium pyrophosphate 20 Each solution contained about0.2% of the above formulation and standardized washing machineconditions were employed, permonosulfate supplying 25 p.p.m. activeoxygen. White cotton cloth swatches at a cloth zwater ratio of 1:20 wereused in the bath at 140 F. and the time of wash cycle was 10 minutes.

, TABLE I Manganese Con- Brightness Units as a Function of Washce(ntratio;1s

The cloth swatches were given a thorough rinse after washing and dried.After the wash and dry cycle, the re flectances of the swatches weredetermined in a Hunter Multipurpose Refiectometer using a blue filter,the fall in reflectance representing a measure of the yellowingfof thefabric. The results show that even small concentrations (about 0.1p.p.m.) of manganese are oxidized and cause yellowing. a;

One method of avoiding discoloration is to eliminate yellow-coloredmanganese ions by reducing the ions to a colorless state. However, it isnecessary to provide a reducing agent that will not .afiect thebleaching action of a'permonosul fateions, i.e., the rate ofreductionmu'st be controlled. Furthermore, it is also necessarythattheagents be "mutually tolerant for at least the jtime required forbleaching and that the reducing agent be c-apableof bleaching, cleansingand laundering. iThese' same sol-u;

tions can be employed to remove the discoloration from materialspreviously yellowed by'highlyoxidized manga neseions H Perhydrates haveall of the above desirablecharactei istics. They may be formulated withalkali metalpefi monosulfiates and simultaneously added to Water; thusused the agents are mutually tolerant for the time period normally usedin all bleaching processes. The agents are sufficiently stable to beincluded in conventional detergent and cleansing formulations and arecompletely safe for home use. Furthermore, the reducing agents areunaffected by the hardness of the water.

Perhydrates are easily prepared by adding H 0 to aqueous salt solutionsand thereafter removing water by drying, leaving crystallineperhydrates. When added to water, perhydrates liberate H 0 and the termperhydrate as used herein refers to compounds so characterized. All ofthese perhydrates are further characterized by functioning as reducingagents in aqueous solutions containing permonosulfate and highlyoxidized manganese (+3 and +4 state of oxidation).

Some well-known compounds that will form perhydrates with H 0 are sodiumborate, aluminum sulfate, urea, sodium acetate, sodium silicate,ammonium carbonate, pyrophosphates and the like. Formulas of persodiumperborate tetrahydrate is NaBO -H -3H O (contains about active "oxygen).The preferred perhydrate is sodiumperborate monohydrate, known as sodiumborate perhydrate, NalBo -H o (contains about 16% active oxygencontent). The alkali metal perborates are disclosed in US. 2,491,789.

The amounts of alkali metal permonosulfate and perhydrate necessary tobe efiective in solution can be conveniently expressed in terms ofactive oxygen ratio. The active oxygen ratio of the permonosulfate tothat of the perhydrate can vary between 3:1 to 30:1 and this ratio iscorrect regardless of the specific permonosulfate 'or perhydrate used.Solutions containing these compounds in amounts based on the above ratioof active 'oxygen are stable and eflective bleaching compositions thatcan be used either to eliminate yellow-colored manganese ions or toavoid yellow discoloration.

EXAMPLE 1 Formulation No. 1 was used in tap water containing about 0.2p.p.m. manganese. An amount of this formulation equal to about 0.2%solution weight was added so that the active oxygen content supplied tothe solution by potassium permonosulfate was about 25 p.p.m. The samestandardized conditions noted above were used. The formulation in thefirst solution included 12% sodium borate perhydrate based on the weightof potassium permonosulfate present.

Residual Brightness UnltsasaFunctlon otWash' Formulation Active No.1Oxygen,

p.p.m. 0 1 2 a 4 5 6 won Sodium Borete Pertime-.- 85.4 85.5 86.3 85.586.1 86.6 86.8- Wg No Reairman... '18 85.9 85.5 85.5 85.5 88.7 82.2 86.2

The next example shows the efiectiveness of sodium perborate inwhitening cloth already yellowed by yellowcolored manganese ions.

EXAMPLE 2 Brightness Units as a Function of Wash Formulation N o. 1

Preferred bleaching conditions are obtained whenpotassiumpermonosul-fate and sodium borate perhydrate are used in combination. Itis obvious, however, that any alkali metal permonosulfate and perhydrateare suitable providing that the active oxygen ratio of the two compoundsare 3:1 to 30: 1, respectively.

As noted'above, some tap water supplies contain 0.1 p.p.m. manganese ormore. The manganese content of tap water is normally not in excess of0.3 p.p.m. and the above formulations will eliminate discoloration insolutions containing these amounts of manganese.

The effect of combining a reducing agent and a strong oxidizing agent toremove discoloration caused by man- ,ganese does not adversely affectthe bleaching efiectiveness of the permonosulfate. Other reducing agentswere inefiective.

Throughout the specification, percentages and parts are calculated on aweight basis unless othenvise designated. The embodiments of theinvention in which an exclusive property or privilege is claimed aredefined as follows; 1. In the method of bleaching with an alkali mepermonosulfate in solution in water containing manganese ions as animpurity, the improvement consisting essentially of incorporating intosaid solution a suflicient amount of a crystalline salt perhydratecompound which liberates hydrogen peroxide in water to reduce saidmanganese ions to a colorless state, the ratio of active oxygen contentof said permonosulfateto said perhydrate being about 3:1 to 30:1. 7

2. 1n the method of bleaching with potassium permonosulfate in solutionin water containing manganese .ions as an impurity, the improvementconsisting essentially of incorporating into said solution a suflicientamount of sodium borate perhydrate to reduce said manganese ions to acolorless state, the ratio of active oxygen content of saidpermonosulfate to said perhydrate being about 3:1 to 30:1.

References Cited in the file of this patent UNITED STATES PATENTSFOREIGN PATENTS 451,025 Great Britain July 27, 1935 451,115 GreatBritain July 29, 1935

1. IN THE METHOD OF BLEACHING WITH AN ALKALI METAL PERMONOSULFATE IN SOLUTION IN WATER CONTAINING MANGANESE IONS AS AN IMPURITY, THE IMPROVEMENT CONSISTING ESSENTIALLY OF INCORPORATING INTO SAID SOLUTION A SUFFICIENT AMOUNT OF A CRYSTALLINE SALT PERHYDRATE COMPOUND WHICH LIBERATES HYDROGEN PEROXIDE IN WATER TO REDUCE SAID MANGANESE IONS TO A COLORLESS STATE, THE RATIO OF ACTIVE OXYGEN CONTENT OF SAID PERMONOSULFATE TO SAID PERHYDRATE BEING ABOUT 3:1 TO 30:1. 